1. Technical Field
The present invention relates to a rolling bearing, a rolling bearing for fuel cell, a compressor for fuel cell system and a fuel cell system. The present invention relates to a fuel cell system which operates to gasify a fuel such as methanol and water, modify the gas in a modifier, remove CO from the gas in a CO remover, and then supply the fuel into a stack of fuel cells (fuel cell main body) where electricity is generated, a fuel cell system which operates to supply hydrogen as a fuel from a hydrogen storage unit such as hydrogen tank and hydrogen storage alloy into a stack of fuel cells where electricity is generated, a fuel cell system which operates to withdraw hydrogen from a hydrogen-containing compound such as methanol and water in a modifier, remove impurities from the fuel in an impurity remover such as CO remover, and then supply hydrogen into a stack of fuel cells where electricity is generated, a compressor for fuel cell system for force-feeding various fluids between various machines in these fuel cell systems, and a rolling bearing for fuel cell system to be incorporated in this compressor. The present invention further relates to a rolling bearing for fuel cell to be incorporated in, e.g., solid polymer electrolyte type fuel cell system.
2. Background Art
A fuel cell allowing exhaustion of clean exhaust gas and high energy efficiency has been noted over the issue of energy supply and environmental problems such as air pollution by emission form automobile and global warming by carbon monoxide. A fuel cell undergoes electrochemical reaction of hydrogen or hydrogen-rich modified gas with an oxidizer such as oxygen (air) to convert chemical energy to electrical energy. Examples of the electrolyte to be incorporated in the fuel cell include solid polymer, aqueous solution of phosphoric acid, molten carbonate, and aqueous alkaline solution. In particular, a solid polymer electrolyte type fuel cell is useful particularly as a power source for transporting body such as automobile, ship and spaceship because it is advantageous in that it can generate electricity at a relatively low temperature (not higher than 100° C.), exhibits a high output density, operates at low temperatures, shows little deterioration of constituents and can be easily started. Various fuel cell systems have been proposed (see JP-A-11-307112).
A solid polymer electrolyte type fuel cell essentially comprises a stack of fuel cells obtained by laminating cells with a separator provided interposed therebetween, said cells each having two gas diffusion electrodes, i.e., porous cathode (oxygen electrode) and anode (fuel electrode) comprising a noble metal such as platinum as a catalyst laminated on each other with a solid polymer electrolyte membrane interposed therebetween. These separators each have a gas passage formed on both surfaces thereof. An oxidizer gas is supplied and discharged through the gas passage on the cathode side. A fuel gas is supplied and discharged through the gas passage on the anode side. Further, since the fuel cell undergoes exothermic reaction, a cooling portion is normally provided each for several cells.
Such a fuel cell system comprising a solid polymer electrolyte type fuel cell employs a compressor to force-feed hydrogen, a hydrogen-rich modified gas and a large amount of air as an oxidizer. Various compressors having improvements for stable force-feeding have been proposed (see JP-A-2002-70762). A compressor comprises a rolling bearing incorporated therein to support the rotary shaft. The rolling bearing has a grease encapsulated therein for lubrication. However, the volatile component can be scattered and attached to the stack of fuel cells to act as a catalyst poison. Compressors which are designed to prevent the scattering and leakage of volatile components have been proposed (see JP-A-2000-2192 and JP-A-2002-70764).